Leaders of California's largest teachers union have launched a new ad campaign, but this time they're not battling for hearts and minds on school policy. They're competing against charter school advocates to get politicians elected to office — with some schoolyard name calling.

In the months leading up to the June primary, the two largest charter school groups spent more than $10.4 million in "independent expenditures" on fourteen races — the most they have spent in this type of political influence in any election cycle since at least 2002.

The spending was an overt strategy to influence primary races. And it was aided by several major donors, including philanthropist Eli Broad who gave more than $1 million dollars. Among the other wealthy donors are Netflix CEO Reed Hastings and Wal-Mart heirs Alice, Jim and Carrie Walton.

The ad campaign the union launched in response last week, dubbed "Kids Not Profits," denounces these contributions; one radio spot claims rich donors are "paying to push their agenda on the rest of us."

The union has only spent $236,000 so far this election season, on two state legislative races, according to data from the Secretary of State's office.

But charter advocates said unions are being hypocritical.

"They have historically, significantly outspent what you have seen us spending thus far in this cycle, for example," said Gary Borden, executive director of the California Charter Schools Association's political arm, CCSA Advocates. "The notion that [the unions] don’t have the capacity to spend significantly in these races is, I think, certainly a fallacy."

The teacher's union is certainly a juggernaut in Sacramento politics, commonly ranking among the biggest campaign donors. But there's conflicting evidence about whether charter school backers have mustered the money to unseat CTA from this perch.

The union is right that charter groups have spent more in 2016 onindependent expenditures — that is, spending on a race by an outside group that isn't coordinated with the affected candidates. It is also true that the union has donated much more in direct contributions to candidates and causes than charter school advocates have.

The two most active pro-charter groups, EdVoice and CCSA Advocates, have together given around $475,000 in direct contributions to candidates, campaigns or other political action committees this year. The CTA has contributed around $1.6 million in direct contributions in 2016. Its smaller counterpart, the California Federation of Teachers, has made around $880,000 in contributions.

In 2013 and 2014, the two teachers unions contributed more than $21.7 million to campaigns. They also spent $7.5 million in 2014 through an independent expenditure committee the CTA set up specifically to support their favored candidate for state schools superintendent, Tom Torlakson.

Borden said CCSA Advocates made a strategic decision to spend heavily during the primary races — especially in state legislative campaigns — because they feared a high-profile presidential contest and other statewide races will drown out local races in the general.

Charter groups spent big during primary races in hopes they'd be more effective in raising their favored candidates' name recognition, Borden said.

The impact of this strategy on the independent expenditure numbers, though, has been stark.

As KPCC reported in June, spending by one pro-charter school group accounted for more than 70 percent of the outside money spent in the contest between Glendale Democrats Ardy Kassakhian and Laura Friedman, both hoping to win the 43rd District seat in the California State Assembly.

The battles closer to home continue as well. Two members of the L.A. school board are up for re-election in March 2017. Board president Steve Zimmer, historically a favorite of teachers union leaders, faces a steep challenge from Nick Melvoin, who has already raised more than $124,000 — including $1,100 from charter supporter Eli Broad. Zimmer has raised around $7,300.

Mónica García, who has received $2,200 from Broad and his wife Edythe, also enjoys a wide fundraising lead over her charter-opposed challenger, Carl Petersen.

But it's still early and the teachers union's ability to mobilize the vote is priceless.

Like the state union, United Teachers Los Angeles, which represents L.A. Unified teachers, recently launched a "public awareness campaign," featuring images of smiling teachers on more than 100 billboards and bus bench ads.

Politically, UTLA sees the campaign as part of the "long game," said the union's secretary, Daniel Barnhart. He said the ads are a response to the same concern the CTA mentions: the growth of charter schools backed by for-profit operators or wealthy political donors.

"We want to raise awareness about the need to support public schools and also to kind of reclaim the narrative. The notion of what it means to be ‘public' has been diluted a little bit," Barnhart said, referring to the union argument that charters siphon public funding away from school districts while being held to different regulatory standards.

"We run the risk of diluting what it means to be a public school or to be in support of public education."